Re: fast NPN in LT Spice

On 4/06/2024 12:18 am, john larkin wrote:

On Mon, 3 Jun 2024 09:58:52 +0200, Jeroen Belleman
<jeroen@nospam.please> wrote:
 

On 6/3/24 00:36, john larkin wrote:

There are many NPNs in the standard LT Spice library.
>
Does anyone know of a fast, RF type, transistor? It's hard to tell
from the jillion lines of fine-print parameters.
>
I want to make a model of the MC10EP89 gate.
>

>
I always used the -now obsolete- BFR92A for such things.
That's a 5GHz Ft NPN that I used often. It's not in the
library, I think. Below the model. Mind the line wraps.
>
Jeroen Belleman
>
.model BFR92A NPN IS=4.11877E-016 BF=1.02639E+002 NF=9.97275E-001
VAF=6.26719E+001 IKF=3.20054E+000 ISE=4.01062E-015 NE=1.57708E+000
BR=1.81086E+001 NR=9.96202E-001 VAR=3.36915E+000 IKR=1.28155E+000
ISC=2.79905E-016       NC=1.07543E+000 RB=1.00000E+001 IRB=1.00000E-006
RBM=1.00000E+001 RE=1.16450E+000 RC=2.32000E+000 EG=1.11000E+000
XTI=3.00000E+000 CJE=8.90512E-013 VJE=6.00000E-001 MJE=2.58570E-001
TF=1.54973E-011 XTF=3.91402E+001 VTF=2.15279E+000       ITF=2.13776E-001
CJC=5.46563E-013 VJC=3.80824E-001 MJC=2.02935E-001

 2SC3838K is in the library, and has Ft = 3.5G typically. It's good
enough for what I want to do now.
 This is actually a bit faster than the MC10EP89:

<snipped two transistor model>
It is worth noting that even 3.5GHz transistors tend to need base-stopper resistors in real life. Collector-base capacitive feedback can make them self-oscillate without it. Phil Hobbs has found two Murata ferrite bead/chips which are specified as presenting resistive impedances of 60R and 200R at 5GHz which seems to do the job too.
Jim Thompson designed that kind of integrated circuit, but he's been dead for a while now.
--
Bill Sloman, Sydney